1. Technical Field
This application relates to a video game program and a video game system and, more particularly, to a video game program and a video game system for playing a video game using an optical pointing device.
2. Background
There are conventional video game systems using optical pointing devices. For example, Patent Document 1 (Japanese Laid-Open Patent Publication No. 8-71252) discloses a shooter video game device using a gun-shaped controller. The gun-shaped controller has a CCD camera for sensing light-emitting members provided, as marker objects, around the video screen. Thus, the video game device can detect the distance between the screen and the gun-shaped controller, the rotation of the gun-shaped controller, and the position thereof. Specifically, Patent Document 1 discloses a shooter video game device capable of calculating the position (the coordinates thereof) on the screen being pointed at by the gun-shaped controller.
Patent Document 2 (Japanese Laid-Open Patent Publication No. 2002-81909) also discloses another shooter video game device employing substantially the same configuration as that of Patent Document 1 (see paragraph 0020, etc.). With this shooter video game device, a position on the screen being pointed at by a gun-shaped controller is calculated by using an image captured by image capturing means provided in the gun-shaped controller. In the shooter video game, the calculated position is used as the position at which a gunsight image of the gun-shaped controller is displayed. There are known video games in which the position on the screen being pointed at by a gun-shaped controller is calculated, and used the position at which a gunsight image is displayed.
With these video game devices, the position on the screen being pointed at by the gun-shaped controller can be calculated, and the gunsight image is displayed at the calculated position on the screen. Therefore, the player can easily know the direction in which the gun is being directed, i.e., the position on the screen being pointed at by the gun-shaped controller. When the markers (light-emitting members) are out of the image capturing area of the image capturing means provided in the gun-shaped controller, it means that the aiming point of the gun-shaped controller is outside the screen, in which case the gunsight image on the screen cannot be moved or controlled. If the image capturing means again starts sensing the markers, the gunsight image will be displayed at the position on the screen pointed at by the gun-shaped controller.
A controller using an optical pointing device as described above has primarily been used for moving a gunsight image on the screen in a shooter video game. Recently, with an increasing variety of types of video games, such a controller may be used for controlling any other object in the game space, in addition to controlling a gunsight image on the screen. For example, there are at least two ways in which an object in a three-dimensional game space is moved by using a controller. In the first way, an object is placed at a position in a three-dimensional game space corresponding to a position on the screen pointed at by the controller, and the object is moved across a two-dimensional plane in the game space according to a two-dimensional movement of the position pointed at by the controller. With this technique, however, the object can only be moved across a two-dimensional plane in the game space, which is not at all different from moving a gunsight image in conventional shooter video games, except that the game space is three-dimensional.
In the second way, the player can move the controller up and down to change the Y coordinate of the object placed in a three-dimensional game space defined in an XYZ coordinate system, thereby moving the object up and down in the game space. The player can move the controller left and right to change the X coordinate of the object in the game space, thereby moving the object left and right in the game space. Moreover, the player can move the controller forward and backward to change the Z coordinate of the object in the game space, thereby moving the object forward and backward in the game space.
In the second way as described above, the object in the three-dimensional game space may not always be displayed at the position on the screen pointed at by, for example, the controller (hereinafter referred to as the “pointed position”, corresponding to the position of the gunsight image on the screen in conventional shooter video game devices). With a typical three-dimensional game space, the game space is shown in a bird's-eye view as viewed from a virtual camera. Therefore, the up/down, left/right and forward/backward movements in the game space do not always coincide with those as viewed from the virtual camera. Specifically, when an object moves in the up/down direction by a certain distance in the game space, the object moves by a shorter distance on the bird's-eye view of the game space as viewed from the virtual camera. When the object moves in the depth direction in the game space, which is the direction away from the virtual camera, the object on the screen as viewed by the virtual camera moves toward the center of the screen. Thus, the position on the screen pointed at by the controller may not coincide with the position at which the object is displayed on the screen.
In conventional shooter video game devices, the gunsight image is displayed at the position pointed at by the controller. Therefore, the player can easily recognize the direction in which the controller is being directed. However, where the controlled object is not displayed at the pointed position, the player cannot recognize the direction in which the controller is being directed. Since the player cannot recognize the pointed position by looking at the screen, the player may move the controller to such a position that the image capturing means of the controller can no longer sense the markers, whereby the object can no longer be controlled. Particularly, if the player cannot identify the current direction of the controller (i.e., the pointed position) when starting to control the object, the player will have to control the object without knowing at all the direction in which the controller is being directed. Therefore, it is likely that the player moves the controller to such a position that the image capturing means of the controller can no longer sense the markers. This also significantly degrades the controllability in using the controller.
As described above, if the display position of an object being controlled by using a controller does not coincide with the position pointed at by the controller, the player may move the controller to such a position that the object can no longer be controlled.